Patent application title: HIGH POWER FUEL CELL

Abstract:

A device for highly efficient fuel cell reactions is described. The device
comprises a porous electrode and a plurality of suspended nanoparticles
diffused within the void volume of the electrode when used within an
electrolyte, wherein each chamber contains an electrode and electrolyte
with suspended nanoparticles therein. When reactive metal particles are
diffused into the electrode structure and suspended in electrolyte by
gasses, a fluidized bed is established, allowing for improved power
generation. Ideally, this device and system can be used to produce high
power output.

Claims:

1. A device suitable for use in at least one fuel cell application, the
device comprising a first component and a second component, the first
component comprising a metal having substantial void volume and where
said first component is at least partially exposed to a reaction medium
during use, the second component comprising a plurality of reactive metal
nanoparticles suspended in the reaction medium and substantially diffused
through the first component when the device is in use.

2. The device of claim 0, wherein at least a substantial portion of the
plurality of reactive metal particles comprises particles have an
effective diameter of less than about 100 nm.

3. The device of claim 0, wherein at least a portion of the reactive metal
particles comprise nanoparticles having an oxide shell.

4. The device of claim 0, wherein the plurality of reactive metal
particles comprise one or more of the metals from groups 3-16,
lanthanides, combinations thereof, and alloys thereof.

5. The device of claim 0, wherein the first component is a sintered porous
metal plate.

6. The device of claim 0, wherein the first component is a reticulate
metal plate.

7. The device of claim 0, wherein the first component comprises one or
more of the metals from groups 3-16, lanthanides, combinations thereof,
and alloys thereof.

8. The device of claim 1, wherein the reaction medium is an alkaline
electrolyte.

9. The device of claim 1, wherein the reaction medium is an acidic
electrolyte.

10. The device of claim 1, wherein the device is configured to generate
electricity from liquid or gaseous fuels.

11. The device of claim 10, wherein the fuel is hydrogen.

12. The device of claim 10, wherein the fuel is oxygen.

13. The device of claim 10, wherein the fuel is ammonia.

14. The device of claim 10, wherein the fuel is a lower alcohol, ester,
ether, or carbonate.

Description:

[0004]A fuel cell is a device that converts chemical energy directly into
electrical energy. They typically operate with higher efficiencies than
traditional combustion engines. In addition, emission of greenhouse
gasses from fuel cells is reduced or eliminated. The prospect of
affordable, clean fuel for stationary and transportation applications are
several of the driving forces behind the Hydrogen Economy, wherein the
energy infrastructure is based on hydrogen instead of oil. Liquid
hydrocarbon fuels, such as methanol, are also advantageous in fuel cells.

[0005]Platinum is highly catalytic for hydrogen or hydrocarbon oxidation
and oxygen reduction in gas diffusion electrodes for a variety of fuel
cells. However, this noble metal is a rapidly depleting non-renewable
resource and is consequently expensive. Current price for bulk platinum
black is $75.00/gram. The associated cost of a platinum deposited
electrode, typically loaded anywhere from 2-8 mg/cm2, is widely
considered to be a hurdle to widespread commercialization. With the
gaining demand for alternative energy sources by consumers, efficient
catalysts, new fuel cell electrodes and designs must be discovered to
alleviate the demand and expense of platinum. Based on this, considerable
effort is being dedicated to find an alternative catalyst which can match
or exceed platinum's electrical performance. Method of synthesis of metal
nanoparticles has been previously described in U.S. patent application
Ser. No. 10/840,409, as well as their use in air cathodes for batteries
in U.S. patent application Ser. No. 10/983,993 both of which applications
have the same assignee as the present application. The disclosures of
these applications are incorporated herein by reference.

SUMMARY OF THE INVENTION

[0006]In one aspect of the invention, a high-surface area electrode is
conceived. In one embodiment, the electrode comprises a porous or
reticulate metal plate combined with catalytic metal particles,
preferably at the nanoscale. The plate preferably includes some void
volume to allow infusion of the nanosized metal particles. When immersed
within an electrolyte, the metal particles can float freely and can
substantially infuse into the porous/reticulate metal plate to create an
electrode with extremely high surface area. This electrode can be applied
to a variety of devices, including a fuel cell system. Essentially, in
such an embodiment, the electrode functions as a fluidized bed. At least
one advantage is that the electrode can be operated at very high current
(rate), which in turn means that larger amounts of energy can be
produced. Typical electrodes have a far lower surface area and thus
cannot provide increased power density. Other advantages may include,
depending upon the configuration, circumstances, and environment, the
ability to scale the electrode to a wide variety of sizes, higher power,
and the ability to minimize agglomeration by using nanosized particles.

[0007]In another embodiment of the invention, a new electrochemical device
is contemplated, preferably a fuel cell device. Unlike traditional fuel
cells, one embodiment of the inventive electrochemical device system may
be oriented horizontally rather than vertically. With such an
arrangement, air/oxygen may be moved through the lower (cathode) chamber,
and enter a catalytic layer through a porous hydrophobic film where it
reacts with water and electrons being consumed and hydroxyl ions
generated on the lower electrode. Excess oxygen may be re-circulated back
into the system. Hydroxyl ions from the reaction can move through a
separator membrane to the upper (anode) chamber, where they recombine
with hydrogen gas to produce water and electrons. Contemporaneously, the
upper chamber electrode is consuming hydrogen gas. Hydrogen gas is
circulated through the upper chamber through a diffuser, and because
hydrogen gas is less dense than the electrolyte, the unreacted hydrogen
may bubble upwards and can then be removed from the system to be
re-circulated back through the diffuser. Preferably, a fluidized bed is
established using hydrogen gas as the fluidizer in the upper chamber
employing catalytic nanoparticles. At least some advantages include,
depending upon the configuration, circumstances, and environment, (i)
pumping only gasses means much lower parasitic losses than if pumping
fluids; (ii) there is no need for a gas separator in the upper chamber;
gas freely moves upward because it is less dense, (iii) all excess
hydrogen and oxygen gas can be re-circulated back into the system,
minimizing reactant loss and increasing efficiency, and (iv) elimination
of precious metal catalysts.

[0008]In yet another aspect of the invention, a fluidized bed electrolyzer
can also be established in a vertical orientation. This device may
consist of a corrosion resistant container that houses a cylindrical
separator. Porous anode and cathode electrodes would be disposed on the
outer and inner circumference of the separator, respectively. The inner
chamber would be filled with electrolyte and preferably contain a
plurality of reactive metal nanoparticles. These reactive metal
nanoparticles establish a fluidized bed in the anode chamber. The cathode
would contain a hydrophobic sheet through which oxygen could flow to
sustain the electron consuming reaction. The hydroxyl ions would migrate
through the vertical, cylindrical separator to react on the anodic
current collector with the anolyte and catalyzed by the fluidized
catalyst particles. At least some advantages of this configuration
include, (i) ease of keeping hydrogen and oxygen gasses separated, (ii)
ease of controlling temperature and pressure, (iii) simple design, (iv)
less expensive per unit of electricity produced, and (v) elimination of
precious metal catalysts. Preferably, a number of vertical orientation
electrolyzers are interconnected to function as an electrolyzer stack.

[0009]In another embodiment of the inventive electrochemical device system
air/oxygen may be moved through one (cathode) chamber, with electrons
being consumed and hydroxyl ions generated on that electrode. Excess
oxygen may be re-circulated back into the system. Preferably, a fluidized
bed is established using oxygen gas as the fluidizer in this cathodic
chamber employing catalytic nanoparticles. Hydroxyl ions from the
reaction can diffuse through a separator membrane to an adjacent (anode)
chamber, where they recombine with hydrogen gas in a current collecting
surface in the presence of catalytic particles and electrolyte to produce
water and electrons. Contemporaneously, this anode chamber electrode
hydrogen gas is circulated through this chamber through a diffuser, and
can be re-circulated back through the diffuser. Preferably, a fluidized
bed is established using hydrogen gas as the fluidizer in this anodic
chamber employing catalytic nanoparticles. At least some advantages
include, depending upon the configuration, circumstances, and
environment, (i) circulating gasses is lower energy than pumping liquids,
so there will be less parasitic losses; (ii) there is no need for an
external gas separator, (iii) all excess hydrogen and oxygen gas can be
re-circulated back into the system, minimizing reactant loss and
increasing efficiency, and (iv) elimination of precious metal catalysts.

[0010]In another aspect of the invention, the cathode electrode used in
the fuel cell is described in U.S. patent pending application Ser. No.
11/482290.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011]FIG. 1 is a schematic of a typical fuel cell.

[0012]FIG. 2 is a fuel cell described in some of the preferred
embodiments.

[0013]FIG. 3 is a fuel cell described in some of the preferred
embodiments.

[0014]The features mentioned above in the summary of the invention, along
with other features of the inventions disclosed herein, are described
below with reference to the drawings of the preferred embodiments. The
illustrated embodiments in the figures listed below are intended to
illustrate, but not to limit the inventions.

DETAILED DESCRIPTION OF SOME PREFERRED EMBODIMENTS

[0015]FIG. 1 illustrates a traditional fuel cell system. The electrodes
are typically oriented in a vertical fashion and are substantially solid.
Oxygen and hydrogen gasses are applied to the cathode and anode
electrodes, respectively. Electrodes are typically solid metal or
electrodeposited metal with relatively low surface area.

[0016]Referring to FIG. 2, one embodiment of an inventive fuel cell
configured to generate electricity from hydrogen and oxygen can be
described. Electrolyte 201, such as aqueous potassium hydroxide (KOH) may
be placed in a first chamber 202 via inlet port 203. When hydroxyl ions
(OH--) come into contact with anode electrode 204, electrons and water
are produced by H2+2OH.sup.-→2H2O+2e-. Electrons move through
circuit to the cathode via electrical circuit 205. Because hydrogen gas
is less dense than the electrolyte, it rises and leaves via port 206 to
be re-circulated back into the upper chamber through diffuser 214. In a
second chamber 208, oxygen is circulated parallel to anode electrode and
over the cathode assembly 207, which consists of a hydrophobic layer,
current collector catalytically active mass and separator via inlet port
211 and outlet port 210. In a preferred operative mode of at least one
system embodiment, the system is oriented such that the first chamber 202
is positioned above the second chamber 208. Such an arrangement provides
some advantages as discussed herein. It is contemplated, however, that
another embodiment may comprise a system that is usefully oriented in
such a manner that the first chamber is horizontally displaced relative
to the second chamber, either in a side-by-side arrangement, or at some
angle between vertical and horizontal.

[0017]When electricity is applied to cathode electrode 207 via electrical
contact 212, and air is circulated through the system, hydroxyl ions
(OH.sup.-) are produced pursuant to the following general reaction:
1/2O2+H2O+2e-→2OH.sup.-. Excess oxygen moves through the
system and can be circulated back into the cell to decrease reactant
loss.

[0018]For some system measurements, a side chamber containing separator
mat 214 is filled with electrolyte 201, and reference electrode 215 is
placed to measure electrochemical potential versus the upper chamber.
Additionally, working reference electrode 216 is placed in contact with
electrode 204.

[0019]In some of the preferred embodiments, the upper chamber features
both an inlet and outlet port. One of the ports allows the removal and
recirculation of hydrogen gas in the system, and the other allows for
direct injection of new electrolyte or new catalyst. This feature allows
for both simple cleaning and replenishment or replacement of catalyst and
reactants.

[0020]A vertical design is also conceived, as shown in FIG. 3. The
hydrogen would need to be circulated out the top and back in the bottom.
The air also needs circulation, but if the outer wall were perforated,
then it may work well in a static condition. In this design, multiple
tubes could be connected for increased power output.

[0021]Some of the preferred embodiments detail an increased available
reaction surface through the use of porous electrodes. The electrodes can
be prepared of networking metal particles, for example reticulate nickel
or nickel foam. In other embodiments, the electrodes may be sintered
metal plates, prepared such that the electrode is highly porous with a
relatively large void volume. The electrodes are preferably prepared from
metals, preferably selected from the group of metals from groups 3-16,
and the lanthanide series. More preferably, the metals are transition
metals, mixtures thereof, and alloys thereof and their respective oxides.
Most preferably, the metal or metals are selected from the group
consisting of nickel, iron, manganese, cobalt, tin, and silver, or
combinations, alloys, and oxides thereof for the cathode chamber and
Nickel, silver, cobalt, tungsten, FeWosub3 and WCosub12 for anodic
catalysts.

[0022]An aspect of at least some of the embodiments in this invention
includes the realization that a reticulate or porous electrode's surface
area can be increased significantly through the use of free moving
reactive metal particles within the electrolyte. The electrolyte serves
as both an ionic conductor and medium for the particles. Because of the
reticulate or porous nature of the electrode, reactive metal particles
can infuse into the electrode surface and become diffuse throughout the
void volumes in the electrode. Preferably, the particles are less than
one micron in effective diameter, and most preferably less than 100
nanometers in diameter. Most preferably, the reactive metal particles are
less than 50 nm in diameter such that substantial portion can infuse into
the electrode. Larger particles tend to agglomerate to the extent that
the void volume within the electrode can no longer accommodate their
size. This results in a significant loss in efficiency.

[0023]Additionally, reactive surface area is increased by order of
magnitude by operation with catalytic nanoparticles in the fluidized bed.
In addition to the surface area of the porous or reticulate electrode,
and nanoparticles infused into the electrode, the system capitalizes on
the additional surface area of the fluidized catalytic nanoparticles. The
increased catalytic behavior of the reactive metal nanoparticles,
compared to the surface of the metal substrate alone, is high due to the
very large number of atoms on the surface of the nanoparticles. By way of
demonstration, consider a 3 nanometer nickel particle as a tiny sphere.
Such a sphere would have 384 atoms on its surface and 530 within its
interior, of the 914 atoms in total. This means that 58% of the
nanoparticles would have the energy of the bulk material and 42% would
have higher energy due to the absence of neighboring atoms. Nickel atoms
in the bulk material have about 12 nearest neighbors while those on the
surface have nine or fewer. A 3 micron sphere of nickel would have 455
million atoms on the surface of the sphere, 913 billion in the low energy
and isolated interior of the sphere for a total of nearly one trillion
atoms. That means that only 0.05% of the atoms are on the surface of the
3 micron-sized material compared to the 42% of the atoms at the surface
of the 3-nanometer nickel particles.

[0025]Another possible technique includes feeding a material onto a heater
element so as to vaporize the material in a well-controlled dynamic
environment. Such technique desirably includes allowing the material
vapor to flow upwardly from the heater element in a substantially laminar
manner under free convection, injecting a flow of cooling gas upwardly
from a position below the heater element, preferably parallel to and into
contact with the upward flow of the vaporized material and at the same
velocity as the vaporized material, allowing the cooling gas and
vaporized material to rise and mix sufficiently long enough to allow
nano-scale particles of the material to condense out of the vapor, and
drawing the mixed flow of cooling gas and nano-scale particles with a
vacuum into a storage chamber. Such a process is described more fully in
U.S. patent Ser. No. 10/840,109, filed May 6, 2004, the entire contents
of which is hereby expressly incorporated by reference.

[0026]The chemical kinetics of catalysts generally depends on the reaction
of surface atoms. Having more surface atoms available will increase the
rate of many chemical reactions such as combustion, electrochemical
oxidation and reduction reactions, and adsorption. Extremely short
electron diffusion paths, (for example, 6 atoms from the particle center
to the edge in 3 nanometer particles) allow for fast transport of
electrons through and into the particles for other processes. These
properties give nanoparticles unique characteristics that are unlike
those of corresponding conventional (micron and larger) materials. The
high percentage of surface atoms enhances galvanic events such as the
splitting of hydrogen or methanol to generate electrons, or the oxygen
reduction reaction.

[0027]The reactive metal particles referenced herein are preferably
selected from the group of metals from groups 3-16, and the lanthanide
series. More preferably, the metals are transition metals, mixtures
thereof, and alloys thereof and their respective oxides. Most preferably,
the metal or metals are selected from the group consisting of nickel,
iron, manganese, cobalt, tin, tungsten and silver, or combinations,
alloys, and oxides thereof. The nanoparticles may be the same as,
substantially the same, or entirely different materials from those chosen
for the electrode. Additionally, the nanoparticles may comprise a metal
core and an oxide shell having a thickness in the range from 5 to 100% of
the total particle composition, wherein the metal core may be an alloy.

[0028]The foregoing description is that of preferred embodiments having
certain features, aspects, and advantages in accordance with the present
inventions. Various changes and modifications also may be made to the
above-described embodiments without departing from the spirit and scope
of the inventions.